Thin-film magnetic discs or media are widely used as data storage media for digital computers. The discs are typically formed by successively sputtering onto a rigid disc substrate and underlayer, a magnetic recording layer and a carbon overcoat which protects the magnetic layer from wear and reduces the frictional forces between the disc and the read.backslash.write head.
It is desirable that such media have excellent magnetic recording properties, for example, a high coercivity, high amplitude and low noise and numerous approaches have been described for improving the magnetic recording performance. One approach has focused on tailoring the underlayer to provide a surface that controls the grain size of the magnetic layer and/or permits epitaxial growth of the magnetic layer.
Approaches to tailoring the underlayer to control the ultimate magnetic recording properties of the disc have included controlling the thickness of the underlayer, the deposition conditions of the underlayer, the composition of the underlayer and/or the number of underlayers present. For example, increasing the thickness of the underlayer has been shown to improve coercivity, up to underlayer thicknesses of several thousand angstroms, e.g. 2,000-5,000 .ANG. (Fisher, et al., IEE Trans. Magn., 22:352 (1986), Johnson, K. E., et al., J. Appl, Phys., 67(9):4686 (1990)). The effect of depositing a chromium underlayer under a substrate bias has been examined (Lal, B. B. et al., IEEE Trans. Magn., 30(6):3954 (1994) and shown to improve coercivity.
Magnetic media having underlayers varying in composition have been described, for example, underlayers composed of chromium-based alloys such as CrMo, CrW, CrV (Ahlert, U.S. Pat. No. 5,051,288). Others have described magnetic media having more than one underlayer as an approach to controlling or improving magnetic recording properties (Shiroishi, et al. U.S. Pat. No. 4,833,020; Suzuki, et al. U.S. Pat. No. 5,316,844). There is still a need, however, for media which have improved recording performance.